1. Field of the Invention
This invention relates generally to an apparatus for measuring the concentricity of workpieces having both a shaft and a drive profile.
2. Summary of the Prior Art
Typical workpieces requiring concentricity measurement include fasteners with internal drive profiles such as slotted, cross, hexagonal, and square recesses; fasteners with external drive profiles, such as hexagonal heads; and other workpieces such a punches which can have either internal or external drive profiles. The concentricity of a workpiece shank to a workpiece drive profile is critical for the operation of modern automated assembly equipment. If the drive profile and shank do not share a common axis, automated assembly equipment will often malfunction and cannot perform efficiently.
Although a wide body of prior art exists describing devices which measure the diameters of threaded and non-threaded cylindrical objects, the prior art describing workpiece concentricity measurement is limited. However, devices capable of measuring the concentricity of screws and punches are marketed.
One prior art device uses a cam-actuated lever arm to hold the workpiece shank between three cylindrical, rotatable members. Two of these members are manually rotated to provide 360 degree rotation of the workpiece about the axis of the workpiece shank. This prior art device is equipped with a screw recess checking attachment having an end which engages the workpiece drive profile, structural elements constraining the attachment to vertical, linear motion, and a second end contacting the probe of a dial test indicator. The dial test indicator measures any non-concentricity of the workpiece while the cylindrical members rotate the workpiece about the axis of the workpiece shank.